diff --git a/src/infra/unhandled-rejections.fatal-detection.test.ts b/src/infra/unhandled-rejections.fatal-detection.test.ts
index 6d5f3f5e9f0..7849688eb49 100644
--- a/src/infra/unhandled-rejections.fatal-detection.test.ts
+++ b/src/infra/unhandled-rejections.fatal-detection.test.ts
@@ -93,6 +93,10 @@ describe("installUnhandledRejectionHandler - fatal detection", () => {
         Object.assign(new Error("DNS resolve failed"), { code: "UND_ERR_DNS_RESOLVE_FAILED" }),
         Object.assign(new Error("Connection reset"), { code: "ECONNRESET" }),
         Object.assign(new Error("Timeout"), { code: "ETIMEDOUT" }),
+        Object.assign(new Error("A request error occurred: getaddrinfo EAI_AGAIN slack.com"), {
+          code: "slack_webapi_request_error",
+          original: { code: "EAI_AGAIN", syscall: "getaddrinfo", hostname: "slack.com" },
+        }),
       ];
 
       for (const transientErr of transientCases) {
diff --git a/src/infra/unhandled-rejections.test.ts b/src/infra/unhandled-rejections.test.ts
index 1770209f41e..6b1e4a19108 100644
--- a/src/infra/unhandled-rejections.test.ts
+++ b/src/infra/unhandled-rejections.test.ts
@@ -92,6 +92,30 @@ describe("isTransientNetworkError", () => {
     expect(isTransientNetworkError(error)).toBe(true);
   });
 
+  it("returns true for Slack request errors that wrap network codes in .original", () => {
+    const error = Object.assign(new Error("A request error occurred: getaddrinfo EAI_AGAIN"), {
+      code: "slack_webapi_request_error",
+      original: {
+        errno: -3001,
+        code: "EAI_AGAIN",
+        syscall: "getaddrinfo",
+        hostname: "slack.com",
+      },
+    });
+    expect(isTransientNetworkError(error)).toBe(true);
+  });
+
+  it("returns true for network codes nested in .data payloads", () => {
+    const error = {
+      code: "slack_webapi_request_error",
+      message: "A request error occurred",
+      data: {
+        code: "EAI_AGAIN",
+      },
+    };
+    expect(isTransientNetworkError(error)).toBe(true);
+  });
+
   it("returns true for AggregateError containing network errors", () => {
     const networkError = Object.assign(new Error("timeout"), { code: "ETIMEDOUT" });
     const error = new AggregateError([networkError], "Multiple errors");
@@ -109,6 +133,18 @@ describe("isTransientNetworkError", () => {
     expect(isTransientNetworkError(error)).toBe(false);
   });
 
+  it("returns false for Slack request errors without network indicators", () => {
+    const error = Object.assign(new Error("A request error occurred"), {
+      code: "slack_webapi_request_error",
+    });
+    expect(isTransientNetworkError(error)).toBe(false);
+  });
+
+  it("returns false for non-transient undici codes that only appear in message text", () => {
+    const error = new Error("Request failed with UND_ERR_INVALID_ARG");
+    expect(isTransientNetworkError(error)).toBe(false);
+  });
+
   it.each([null, undefined, "string error", 42, { message: "plain object" }])(
     "returns false for non-network input %#",
     (value) => {
diff --git a/src/infra/unhandled-rejections.ts b/src/infra/unhandled-rejections.ts
index f20fd34409a..fd3f3c966e7 100644
--- a/src/infra/unhandled-rejections.ts
+++ b/src/infra/unhandled-rejections.ts
@@ -35,6 +35,25 @@ const TRANSIENT_NETWORK_CODES = new Set([
   "UND_ERR_BODY_TIMEOUT",
 ]);
 
+const TRANSIENT_NETWORK_ERROR_NAMES = new Set([
+  "AbortError",
+  "ConnectTimeoutError",
+  "HeadersTimeoutError",
+  "BodyTimeoutError",
+  "TimeoutError",
+]);
+
+const TRANSIENT_NETWORK_MESSAGE_CODE_RE =
+  /\b(ECONNRESET|ECONNREFUSED|ENOTFOUND|ETIMEDOUT|ESOCKETTIMEDOUT|ECONNABORTED|EPIPE|EHOSTUNREACH|ENETUNREACH|EAI_AGAIN|UND_ERR_CONNECT_TIMEOUT|UND_ERR_DNS_RESOLVE_FAILED|UND_ERR_CONNECT|UND_ERR_SOCKET|UND_ERR_HEADERS_TIMEOUT|UND_ERR_BODY_TIMEOUT)\b/i;
+
+const TRANSIENT_NETWORK_MESSAGE_SNIPPETS = [
+  "getaddrinfo",
+  "socket hang up",
+  "network error",
+  "network is unreachable",
+  "temporary failure in name resolution",
+];
+
 function getErrorCause(err: unknown): unknown {
   if (!err || typeof err !== "object") {
     return undefined;
@@ -42,6 +61,32 @@ function getErrorCause(err: unknown): unknown {
   return (err as { cause?: unknown }).cause;
 }
 
+function getErrorName(err: unknown): string {
+  if (!err || typeof err !== "object") {
+    return "";
+  }
+  const name = (err as { name?: unknown }).name;
+  return typeof name === "string" ? name : "";
+}
+
+function extractErrorCodeOrErrno(err: unknown): string | undefined {
+  const code = extractErrorCode(err);
+  if (code) {
+    return code.trim().toUpperCase();
+  }
+  if (!err || typeof err !== "object") {
+    return undefined;
+  }
+  const errno = (err as { errno?: unknown }).errno;
+  if (typeof errno === "string" && errno.trim()) {
+    return errno.trim().toUpperCase();
+  }
+  if (typeof errno === "number" && Number.isFinite(errno)) {
+    return String(errno);
+  }
+  return undefined;
+}
+
 function extractErrorCodeWithCause(err: unknown): string | undefined {
   const direct = extractErrorCode(err);
   if (direct) {
@@ -50,6 +95,44 @@ function extractErrorCodeWithCause(err: unknown): string | undefined {
   return extractErrorCode(getErrorCause(err));
 }
 
+function collectErrorCandidates(err: unknown): unknown[] {
+  const queue: unknown[] = [err];
+  const seen = new Set<unknown>();
+  const candidates: unknown[] = [];
+
+  while (queue.length > 0) {
+    const current = queue.shift();
+    if (current == null || seen.has(current)) {
+      continue;
+    }
+    seen.add(current);
+    candidates.push(current);
+
+    if (!current || typeof current !== "object") {
+      continue;
+    }
+
+    const maybeNested: Array<unknown> = [
+      (current as { cause?: unknown }).cause,
+      (current as { reason?: unknown }).reason,
+      (current as { original?: unknown }).original,
+      (current as { error?: unknown }).error,
+      (current as { data?: unknown }).data,
+    ];
+    const errors = (current as { errors?: unknown }).errors;
+    if (Array.isArray(errors)) {
+      maybeNested.push(...errors);
+    }
+    for (const nested of maybeNested) {
+      if (nested != null && !seen.has(nested)) {
+        queue.push(nested);
+      }
+    }
+  }
+
+  return candidates;
+}
+
 /**
  * Checks if an error is an AbortError.
  * These are typically intentional cancellations (e.g., during shutdown) and shouldn't crash.
@@ -88,28 +171,38 @@ export function isTransientNetworkError(err: unknown): boolean {
   if (!err) {
     return false;
   }
+  for (const candidate of collectErrorCandidates(err)) {
+    const code = extractErrorCodeOrErrno(candidate);
+    if (code && TRANSIENT_NETWORK_CODES.has(code)) {
+      return true;
+    }
 
-  const code = extractErrorCodeWithCause(err);
-  if (code && TRANSIENT_NETWORK_CODES.has(code)) {
-    return true;
-  }
+    const name = getErrorName(candidate);
+    if (name && TRANSIENT_NETWORK_ERROR_NAMES.has(name)) {
+      return true;
+    }
 
-  // "fetch failed" TypeError from undici (Node's native fetch).
-  // Treat as transient regardless of nested cause code because causes vary
-  // across runtimes and can be unclassified even for real network faults.
-  if (err instanceof TypeError && err.message === "fetch failed") {
-    return true;
-  }
+    if (candidate instanceof TypeError && candidate.message === "fetch failed") {
+      return true;
+    }
 
-  // Check the cause chain recursively
-  const cause = getErrorCause(err);
-  if (cause && cause !== err) {
-    return isTransientNetworkError(cause);
-  }
-
-  // AggregateError may wrap multiple causes
-  if (err instanceof AggregateError && err.errors?.length) {
-    return err.errors.some((e) => isTransientNetworkError(e));
+    if (!candidate || typeof candidate !== "object") {
+      continue;
+    }
+    const rawMessage = (candidate as { message?: unknown }).message;
+    const message = typeof rawMessage === "string" ? rawMessage.toLowerCase().trim() : "";
+    if (!message) {
+      continue;
+    }
+    if (TRANSIENT_NETWORK_MESSAGE_CODE_RE.test(message)) {
+      return true;
+    }
+    if (message === "fetch failed") {
+      return true;
+    }
+    if (TRANSIENT_NETWORK_MESSAGE_SNIPPETS.some((snippet) => message.includes(snippet))) {
+      return true;
+    }
   }
 
   return false;